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lead us only to condemn waters which had been contaminated with infective sewage. But if a water is contaminated with harmless sewage to-day, it may be fouled with infective sewage to-morrow; and thus the utter worthlessness of the idea that the aim of bacteriology applied to water consists in discovering pathogenic organisms is apparent.

[For discussion on this paper see page 388.]

On "Water Analysis," by Louis PARKES, M.D., Public Health Cert. Lond., Assistant to the Professor of Hygiene and Demonstrator in the Hygienic Laboratory, Univ. Coll.,

London.

THE practice of submitting to an analyst samples of water used, or intended to be used, for drinking purposes, is one undoubtedly much in favour amongst the public. The householder who has read of the dangerous pollutions to which water in wells or cisterns is liable, wishes to know as regards his own domestic arrangements whether the water he drinks is pure and free from suspicion of contamination. He collects some of the water in a bottle and sends it to an analytical chemist for his opinion on the matter. In the course of time a report is received, couched in language and figures unintelligible for the most part to the lay comprehension, but with a few sentences at its termination approving or condemning the water on the results of the analysis; and on this opinion the householder proceeds to act. His faith in the purity of the water is either restored or it is shattered, with the result of his making extensive alterations in the water arrangements of the house, or else seeking a new source of supply. The question therefore of the extent to which chemists and sanitary experts are justified in forming definite conclusions as to the safe or dangerous characters of waters submitted to them for examination is one of considerable interest to the public generally.

Broadly speaking, there may be said to be three methods of examining water, as regards its fitness for domestic use:

1. Physical Examination, by which such qualities as its appearance (colour, clearness, lustre), its taste and its smell are determined. No one thinks of relying solely on the colour or smell of a water when he wishes to form an opinion about its

fitness for drinking; so that although this examination, being easily and rapidly made, is always included in every scheme of water analysis, the indications it gives are necessarily only confirmatory of the other results that may be obtained. The microscopical examination of the sediment deposited by a turbid water should also be included in the physical examination; but of this we shall have to speak further on.

2. The Quantitative Examination of dissolved solids in the water by chemical analysis, is the second method; and

3. The Biological Examination, which is concerned with the quantitative estimation in the water of living micro-organisms belonging to the Bacteria and allied species is the third method.

It will be necessary, owing to the limited time at our disposal, to confine our attention to that aspect of the subject which is connected with the determination of the possible organic pollutions of a water; and, indeed, it is only on this question that any misconception exists. No one denies that the presence of inorganic salts in a water-salts which may render it, from their excessive amount or poisonous natures, unfit for drinking-can be determined accurately by the chemist. The chemist can and does rightly condemn the water which is brackish from infiltration of sea salts, or that which contains excess of lime and magnesian salts, causing an undesirable or positively injurious amount of hardness, or the water which in its passage through various strata may have taken up traces of lead, copper, or arsenic. In such cases as these there is no room for controversy, but it is in those cases where an opinion is desired on the nature and extent of the organic pollutions that a water has been subjected to, that the scientific mind has been so deeply stirred. The question is not yet settled, nor is it likely to be, until our knowledge is more extensive and more accurate; but in the meantime a review of the matter in its larger aspects may not be out of place.

Firstly, it will be well to consider what it is the analyst wishes to determine when he is dealing with the possible organic pollutions of a sample of water submitted to him. He wishes to determine (a) the amount of organic matter present in a measured volume of water, and (b) the nature of this organic matter, i.e., its source or origin, and its potentialities for evil. Does chemical analysis enable these two apparently simple points to be correctly determined? First, as regards (a) the amount of organic matter present. No one who has looked into the subject at all needs to be told that no simple method of estimating organic matter has yet been devised. There is no reagent which can be used as a quantitative test for organic matter, for the simple reason that there is such a numberless

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variety of substances all conveniently included under the generic term "organic," that no single chemical reagent could possibly have the same affinities for all of them, and consequently whilst it might give correct indications of the amount and sence of one or more of them, it could not possibly do so for all. No doubt the Potassium Permanganate solution can-as the test is now carried out-be trusted to estimate approximately the amount of oxidisable organic matters present in the water. But those matters which are oxidisable by Permanganate of Potassium solution are not the only matters of organic origin which may be present; we do not know what proportion they form to the total organic matters, nor do we know whether their deleterious properties are greater or less than those of the non-oxidisable matters.

Failing in our efforts to identify organic matters as such in a water, two methods have been devised for their estimation from the amounts of some of their constituents-processes involving in the one case the breaking up of the complex organic molecule into the simple compound ammonia, by means of destructive distillation with a strongly alkaline solution of permanganate of potassium; and in the other the resolution of the organic matter into its primitive elements carbon (or more accurately carbonic acid) and nitrogen, by means of heat applied to the dry residue obtained from a measured volume of water by evaporation. The first process-the joint invention of Wanklyn, Chapman, and Smith is known as the "albuminoid ammonia process," because albumen is one of the principal substances which yield ammonia on distillation with an alkaline solution of permanganate of potash. The second, or combustion process, is due to the inventive genius of Frankland and Armstrong. There can be no doubt that theoretically, and considered from a philosophical standpoint, Frankland's process should give better results than Wanklyn's. In the former, all the organic matter present is acted upon-none can escape. In the latter, the whole of the nitrogen contained in the nitrogenised organic matters is not converted into ammonia, for whilst permanganate of potash acts powerfully on some kinds of organic matter, it has little or no effect upon others, and the non-nitrogenised organic matters are left out of account altogether. Thus the results obtained have not an absolute significance as they have in Frankland's process, but only a relative. Is this a drawback in actual practice when Wanklyn's process is in use? From Dr. Cory's experiments* it would appear that it is, for he found that the results of different analyses were not comparable with each other except

* Report of the Medical Officer of the Local Government Board, 1881.

under certain conditions, as when the polluting material was of the same nature in all; but on the other side plenty of evidence is to hand showing that under the conditions met with in actual practice the process is to be relied on, especially in estimating those very minute quantities of organic matter which alone are usually found in natural waters. I would more particularly refer to the experiments of Mr. Cassal and Dr. Whitelegge on the quantitative estimation of egg-albumen in water by Wanklyn's process-experiments which throw some doubt on the conclusions arrived at by Dr. Cory from his own experiments. When the polluting ingredients are relatively very large in amount, there can be no doubt that considerable increases or decreases in the amounts of organic matter are not shown in an exactly proportional increase or decrease of albuminoid ammonia. But this is not a matter of practical importance, for if it is right to condemn a water which shows more albuminoid ammonia than the minimum taken as a standard by Wanklyn from his own experience, then it cannot much matter whether the albuminoid ammonia exceeds by 50 times or only by 20 times the allotted amount. Wanklyn's process is easily learnt and easily worked, whilst Frankland's is most difficult except in the hands of the most expert it may give an error of experiment greater than the total quantity to be measured.

But after all it is not the amount of organic matter in a water which renders it harmful, but its kind; and hence the folly of setting up a minimum standard, as Wanklyn has done, for every adversary to tilt at. Our food consists very largely of organic matters, and we ought not to object to taking food and water together, were it not that experience has shown that the organic matter in water is often derived from food materials which have already once passed through the human body, acquiring thereby a potentiality for mischief not to be lightly risked.

We have seen then that chemical processes enable us, in one way or another, to estimate the amount of organic matters in a water-more or less roughly it may be, but still sufficiently for the purpose. Do they give us any information as to the kind of organic matter present? To a certain extent they do; for by their means we can in most cases discriminate the origin of. the organic matter, that is to say, its derivation from the animal or vegetable kingdom. When the pollution is of vegetable origin, chlorides and free ammonia are usually present to

*Remarks on the analysis of water for sanitary purposes. Transactions of the Society of Medical Officers of Health, 1884.

only a slight extent. By Frankland's method under such circumstances it is found that the ratio of organic carbon to organic nitrogen is high, whilst by Wanklyn's the proportion of albuminoid ammonia to free or saline ammonia is relatively large. When the pollution is derived from an animal source, and more especially when it is derived from sewage infiltration, owing to the large amount of common salt and ammonia from decomposed urea found in urine, chlorides and free ammonia are present in excess, the free ammonia that is distilled over greatly exceeds the albuminoid ammonia, and the ratio of organic carbon to organic nitrogen is low. Microscopic examination of the sediment greatly aids in this determination. In the one case fragments of decaying vegetable structure and the minute forms of aquatic life which find a habitat in such materials may be found; whilst in the other, objects such as fibres of linen and cotton, hairs, epidermic scales, &c., which are characteristic of excretal and waste refuse, may be discerned. It is possible then in most cases to distinguish by chemical processes, with the aid of the microscope, between pollutions of animal and vegetable origin; and this distinction is an important one, for there can be no doubt that pollutions caused by sewage infiltration, by soakage from graveyards, or by decomposing animal bodies, are infinitely more dangerous than the pollutions arising from decaying plants and the organisms that thrive amongst them. But these latter must not be thought of as harmless. Ague, intermittent fevers, and dysentery are propagated by drinking vegetably-polluted waters, and we cannot tell whether the specific virus of one of these disorders may not be lurking amongst the more innocent matter.

Supposing it to be allowable to pass as satisfactory a water contaminated to a slight extent with vegetable matter-on the ground that such waters can usually be drunk without the slightest fear of injury, and that therefore a minimum standard of pollution under such circumstances may be a very necessary thing, it must be admitted that there can be no reason why a water which is reasonably believed to be polluted with sewage or other animal emanations should not be condemned at once, however small the pollution may be. It may be said that large numbers of people are continually in the habit of taking sewage into their systems along with their drinking water—the circular system of water-supply from cesspool to well, and again from well to cesspool through the human body being all too common, -but all scientific history proves that such people are walking on the brink of a precipice which may at any time crumble away and precipitate them into the depths below. The difficulty in water analysis is, in many cases, to distinguish between

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